U.S. patent application number 10/263253 was filed with the patent office on 2003-04-24 for air clamp stabilizer for continuous web materials.
Invention is credited to Axelrod, Steven, Luis, Jenson, Moeller, Stefan.
Application Number | 20030075293 10/263253 |
Document ID | / |
Family ID | 26949735 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030075293 |
Kind Code |
A1 |
Moeller, Stefan ; et
al. |
April 24, 2003 |
Air clamp stabilizer for continuous web materials
Abstract
A device for non-contact support of a continuous moving web of
material employs an air clamp stabilizer that includes a Coanda
slot and a backstep that is located downstream of the direction of
the airflow extending from the Coanda slot. This configuration
permits a Coanda jet to expand and to create an additional suction
force. Vortex formation may also occur which further contributes to
the strength of the suction force. As the web passes the
stabilizer, an area of the web material rides on an air bearing
that is maintained above the stabilizer surface and downstream of
the backstep.
Inventors: |
Moeller, Stefan; (San Jose,
CA) ; Axelrod, Steven; (Los Altos, CA) ; Luis,
Jenson; (San Jose, CA) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
26949735 |
Appl. No.: |
10/263253 |
Filed: |
October 2, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60345860 |
Oct 24, 2001 |
|
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|
Current U.S.
Class: |
162/193 ;
162/198; 226/7; 226/97.3; 34/114; 34/116 |
Current CPC
Class: |
B65H 23/24 20130101;
D21F 1/42 20130101; D21F 5/187 20130101; B65H 20/14 20130101 |
Class at
Publication: |
162/193 ;
162/198; 226/97.3; 226/7; 34/114; 34/116 |
International
Class: |
D21F 001/36; D21F
013/00; B65H 020/14 |
Claims
1. A device for non-contact support of a continuous web that is
moving in a downstream direction that comprises: (a) a body having
an operative surface facing the web wherein the operative surface
has an upper portion and a lower portion that is downstream from
the upper portion and wherein the body defines a slot that is in
fluid communication with a source of gas and that has an opening at
the upper surface, and wherein the slot has a curved convex surface
at the opening on its downstream side; and (b) means for directing
a gas from the gas source through the slot so that a jet of gas
moves through the opening and toward the lower portion whereby a
low pressure field is established as the gas passes from the upper
portion to the lower portion thereby maintaining a portion of the
moving web at a substantially fixed distance to the operative
surface.
2. The device of claim 1 wherein the upper portion is vertically
spaced from the lower portion.
3. The device of claim 1 wherein the upper portion and the lower
portion are parallel to each other and the surface connecting the
upper portion to the lower portion defines a plane that is
perpendicular to the upper portion and lower portion.
4. The device of claim 3 wherein the vertical distance between the
upper portion to the lower portion is about 100 .mu.m to 1000 about
.mu.m.
5. The device of claim 1 wherein the surface connecting the upper
portion and the lower portion is a concavely curved surface.
6. The device of claim 1 wherein the body defines a plenum and the
means for directing the gas comprises a pump that pumps gas through
the plenum and into the slot.
7. The device of claim 1 wherein the gas discharged from the slot
at a velocity of about 50 m/s to about 80 m/s.
8. The device of claim 1 wherein the gas in air.
9. The device of claim 1 wherein the slot comprises an elongated
opening with a length that is transverse to the direction of the
moving web.
10. The device of claim 9 further comprising means for adjusting
the width of the opening.
11. The device of claim 10 wherein the opening separates the upper
portion of the body into an upstream portion and a downstream
portion, and wherein the upstream portion is pivotally attached to
the body to permit adjustment of the width of the opening.
12. The device of claim 9 wherein the opening has a width of about
75 .mu.m to 100 about .mu.m.
13. The device of claim 1 wherein at least a portion of the moving
web is maintained at a distance of about 400 .mu.m to about 800
.mu.m above the surface of the body.
14. The device of claim 1 wherein the web is moving at a speed of
about 800 m/min to about 2700 m/min.
15. The device of claim 1 wherein the curved convex surface has a
radius of curvature of about 1.6 mm to about 10 mm.
16. The device of claim 1 wherein the web comprises paper.
17. A method of maintaining a continuous web that is moving in a
downstream direction and in a prescribed orientation relative to a
reference position that comprises the steps of: (a) positioning a
web stabilizer below the moving web wherein the stabilizer
comprises body having an operative surface facing the web wherein
the operative surface has an upper portion and a lower portion that
is downstream from the upper portion and wherein the body defines a
slot that is in fluid communication with a source of gas and that
has an opening at the upper surface, and wherein the slot has a
curved convex surface at the opening on its downstream side; and
(b) directing a gas from the gas source through the slot so that a
jet of gas moves through the opening and toward the lower portion
whereby a low pressure field is established as the gas passes from
the upper portion to the lower portion thereby maintaining a
portion of the moving web at a substantially fixed distance to the
operative surface.
18. The method of claim 17 wherein the upper portion is vertically
spaced from the lower portion.
19. The method of claim 17 wherein the upper portion and the lower
portion are parallel to each other and the surface connecting the
upper portion to the lower portion defines a plane that is
perpendicular to the upper portion and lower portion.
20. The method of claim 19 wherein the vertical distance between
the upper portion to the lower portion is about 100 .mu.m to 1000
about .mu.m.
21. The method of claim 17 wherein the surface connecting the upper
portion and the lower portion is a concavely curved surface.
22. The method of claim 17 wherein the body defines a plenum and
the means for directing the gas comprises a pump that pumps gas
through the plenum and into the slot.
23. The method of claim 17 wherein the gas discharged from the slot
at a velocity of about 50 m/s to about 80 m/s.
24. The method of claim 17 wherein the gas in air.
25. The method of claim 17 wherein the slot comprises an elongated
opening with a length that is transverse to the direction of the
moving web.
26. The method of claim 25 wherein the body further comprising
means for adjusting the width of the opening.
27. The method of claim 26 wherein the opening separates the upper
portion of the body into an upstream portion and a downstream
portion, and wherein the upstream portion is pivotally attached to
the body to permit adjustment of the width of the opening.
28. The method of claim 25 wherein the opening has a width of about
75 .mu.m to 100 about .mu.m.
29. The method of claim 17 wherein at least a portion of the moving
web is maintained at a distance of about 400 .mu.m to about 800
.mu.m above the surface of the body.
30. The method of claim 17 wherein the web is moving at a speed of
about 800 m/min to about 2700 m/min.
31. The method of claim 17 wherein the curved convex surface has a
radius of curvature of about 1.6 mm to about 10 mm.
32. The method of claim 17 wherein the web comprises paper.
33. The method of claim 17 wherein the moving web is maintained as
a flat profile in both a machine direction and a cross direction.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application Serial No. 60/345,860 filed on Oct. 24, 2001.
FIELD OF THE INVENTION
[0002] The present invention relates to an air stabilizer apparatus
for non-contact support of a moving, continuous web of material.
The air stabilizer imparts a force on the continuous web thereby
maintaining the web material in a relatively flat profile as the
web passes over the air stabilizer. This permits accurate
measurements of web properties at the flat profile. The apparatus
is particularly suited for use in the manufacture and processing of
paper products.
BACKGROUND OF THE INVENTION
[0003] In the art of making paper with modern high-speed machines,
sheet properties must be continually monitored and controlled to
assure sheet quality and to minimize the amount of finished product
that is rejected. The sheet variables that are most often measured
include basis weight, moisture content, and caliper, i.e.,
thickness, of the sheets at various stages in the manufacturing
process. These process variables are typically controlled by
adjusting the feedstock supply rate at the beginning of the
process, regulating the amount of steam applied to the paper near
the middle of the process, and/or varying the nip pressure between
calendaring rollers at the end of the process. Papermaking devices
are well known in the art and are described, for example, in
"Handbook for Pulp & Paper Technologists" 2nd ed., G. A. Smook,
1992, Angus Wilde Publications, Inc. Sheetmaking systems are
further described, for example, in U.S. Pat. No. 5,853,543 "Method
for Monitoring and Controlling Water content in Paper Stock in a
Paper Making Machine," U.S. Pat. No. 5,891,306 "Electromagnetic
Field Perturbation Sensor and Methods for Measuring Water Contents
in Sheetmaking Systems," and U.S. Pat. No. 6,080,278 "Fast CD and
MD Control in a Sheetmaking Machine," which are all assigned to the
common assignee of the instant application.
[0004] In the manufacture of paper on continuous papermaking
machines, a web of paper is formed from an aqueous suspension of
fibers (wet stock) on a traveling mesh wire or fabric and water
drains by gravity and vacuum suction through the fabric. The web is
then transferred to the pressing section where more water is
removed by dry felt and pressure. The web next enters the dryer
section where steam heated dryers and hot air completes the drying
process. The papermaking machine is essentially a de-watering,
i.e., water removal, system. In the sheetmaking art, the term
machine direction (MD) refers to the direction that the sheet
material travels during the manufacturing process, while the term
cross direction (CD) refers to the direction across the width of
the sheet which is perpendicular to the machine direction.
[0005] Conventional methods for controlling the quality, e.g.,
basis weight, of the paper produced include regulating the paper
stock, e.g., chemical composition and/or quantity, at the wet end
of the papermaking machine. For example, the thickness of the paper
at the dry end can be monitored to control the flow rate of wet
stock that goes through valves of a headbox and onto the mesh
wire.
[0006] In order to precisely measure some of the paper's
characteristics, it is essential that the fast moving web of paper
be stabilized at the point of measurement to present a consistent,
flat profile since the accuracy of many measurement techniques
requires that the web stay within certain limits of flatness,
height variation and flutter. Moreover, to avoid paper degradation,
stabilization must be accomplished without contact to the
stabilizing device. This is critical at the high speeds which web
material such as paper is manufactured.
[0007] Current non-contact sheet stabilizers fall into two general
categories on the basis of their characteristic operation. The
first category includes various air clamps that use only airflow to
impart some degree of suction on the web material to urge the web
material against a flat surface of the device. These air clamps
have a tendency to leave marks or otherwise damage the moving web.
The second category includes air clamps that use airflow to impart
suction but that also generate an air bearing between a surface on
the device and the web material. The latter category of stabilizers
is exemplified by Vortex, Coanda and Bernoulli-type air clamps
which cushion the moving web material with an air bearing as the
web travels over the device. Vortex-type air clamps provide
adequate air bearing support but create a "sombrero-type" profile
on the web material in the center of its effective region, thus
they do not generate a sufficiently flat profile. Bernoulli-type
air clamps, which blow air out of recessed openings horizontally
over a surface, cause the web material to contact the surface and
flutter. Finally, simple Coanda slot-type air clamps provide an air
bearing and a flat profile adjacent the Coanda slot but lack the
ability of retaining sufficient sheet flatness along the flow
direction away from the Coanda slot. The Coanda effect is a
phenomenon whereby a high velocity jet of liquid issuing from a
narrow slot will adhere to a surface it is traversing and will
follow the contour of the surface.
[0008] As is apparent, the art is in need of a non-contact air
clamp stabilizer for fast moving web materials that is able to
present a flat profile of the web for analysis and that is robust
in response to changes in web (machine) speed and/or weight.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to an air clamp stabilizer
having an operative surface that defines a Coanda slot and a
"backstep" that is located downstream of the direction of the
airflow that extends from the Coanda slot. This novel
configuration, among other things, permits the Coanda jet to expand
and to create an additional suction force. Under certain
circumstances, a vortex is also generated which further contributes
to the suction force. The result is that a defined area of web
material rides on an air bearing as the web passes over the air
clamp surface. This area of the web remains flat and is parallel to
the air clamp surface.
[0010] In one embodiment, the invention is directed to a device for
non-contact support of a continuous web that is moving in a
downstream direction that includes:
[0011] (a) a body having an operative surface facing the web
wherein the operative surface has an upper portion and a lower
portion that is downstream from the upper portion and wherein the
body defines a slot that is in fluid communication with a source of
gas and that has an opening at the upper surface, and wherein the
slot has a curved convex surface at the opening on its downstream
side; and
[0012] (b) means for directing a gas from the gas source through
the slot so that a jet of gas moves through the opening and toward
the lower portion whereby a low pressure field is established as
the gas passes from the upper portion to the lower portion thereby
maintaining a portion of the moving web at a substantially fixed
distance to the operative surface.
[0013] In another embodiment, the invention is directed to a method
of maintaining a continuous web that is moving in a downstream
direction and in a prescribed orientation relative to a reference
position that includes the steps of:
[0014] (a) positioning a web stabilizer below the moving web
wherein the stabilizer comprises body having an operative surface
facing the web wherein the operative surface has an upper portion
and a lower portion that is downstream from the upper portion and
wherein the body defines a slot that is in fluid communication with
a source of gas and that has an opening at the upper surface, and
wherein the slot has a curved convex surface at the opening on its
downstream side; and
[0015] (b) directing a gas from the gas source through the slot so
that a jet of gas moves through the opening and toward the lower
portion whereby a low pressure field is established as the gas
passes from the upper portion to the lower portion thereby
maintaining a portion of the moving web at a substantially fixed
distance to the operative surface.
[0016] It has been demonstrated that the stabilization or flatness
of the web material profile is independent of the web material
speed over a broad range. The inventive stabilizer can be employed
to manipulate the web material into a non-contacting relatively
flat profile where measurements of the web materials
characteristics can be taken with various contact-free measurements
techniques.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross sectional view of one embodiment of the
air clamp stabilizer;
[0018] FIG. 2 is a perspective view of a second air clamp
stabilizer;
[0019] FIG. 3 is a perspective view of the second air clamp
stabilizer in disassembled form;
[0020] FIG. 4 is a cross-sectional view of the second air clamp
stabilizer;
[0021] FIG. 5 is a partial cross-sectional view of the second air
clamp stabilizer;
[0022] FIG. 6 is a graph of the paper profile over the Coanda
slot-backstep portion of the air clamp;
[0023] FIG. 7 is a graph of the paper profile over a simple Coanda
slot without a backstep;
[0024] FIG. 8 is a graph of the paper profile over the Coanda
slot-backstep portion of the air clamp at different paper speeds;
and
[0025] FIG. 9 is a graph of suction pressure versus slot width to
curvature ratio for an air clamp stabilizer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] An embodiment of the air clamp stabilizer 10, as shown in
FIG. 1, includes a body having an operative surface that is
segmented into upstream upper surface 12A and downstream upper
surface 12B and a lower surface 14. Upper surfaces 12A and 12B are
separated by a Coanda slot 18. Upper surface 12B is disposed above
lower surface 14 so that wall or backstep 16 is perpendicular with
respect to both upper surface 12B and lower surface 14 which are
typically coplanar. The stabilizer is positioned underneath a web
of material 38 which is moving from left to right relative to the
stabilizer; this direction is referred to as the downstream
direction and the opposite direction is the upstream direction.
[0027] As will be further described herein, a web that is being
supported by the stabilizer will exhibit a substantially planar
profile at a location above lower surface 14 and downstream from
backstep 16. Preferably an instrument for measuring particular
properties of the web is positioned so that its sensor will make
the measurements at this location. To correctly position the
sensor, lower surface 14 immediately below this location can be
made of an optically reflective material, such as polished
ceramics. In this fashion, the position of the sensor can be
appropriately adjusted, if necessary, before operations with the
moving web. It is understood, however, that the instrument can be
positioned anywhere above the operative surface of the stabilizer
or downstream or upstream thereof, as desired.
[0028] The term "backstep" is meant to encompass a depression on
the stabilizer surface located a distance downstream from Coanda
slot 18 preferably sufficient to create a vortex. As demonstrated
herein, the combination of the Coanda slot and backstep generates
an amplified suction force and an extensive air bearing.
Specifically, backstep 16 allows a Coanda jet to expand and create
an additional suction force. It should be noted that jet expansion
is necessary to create the suction force but vortex formation is
not a prerequisite. Indeed, vortex formation does not always occur
downstream from the backstep and is not necessary for operation of
the air clamp stabilizer. The stabilizer's suction force initially
draws the web closer to the stabilizer as the web approaches the
stabilizer. Subsequently, the air bearing supports and reshapes the
web so that the web exhibits a relatively flat profile as it passes
over the backstep. While backstep 16 is most preferably configured
as a 90 degrees vertical wall as shown in FIG. 1, the backstep can
exhibit a more gradual contour so that the upper and lower surfaces
can be joined by a smooth, concavely curved surface.
[0029] The body of the stabilizer also includes chamber 30 that has
an opening or Coanda slot 18 between upper surfaces 12A and 12B.
Coanda slot 18 has a curved surface 22 on its downstream side.
Preferably this surface has a radius of curvature (R) ranging from
about 1.0 mm to about 10 mm. Chamber 30 is connected to plenum
chamber 20 which in turn is connected to a source of gas 24 via
conduit 36. The volume of gas flowing into plenum 20 can be
regulated by conventional means including flow meter 26 and
pressure gauge 28. The length of chamber 30, as measured along the
cross direction, preferably matches that of Coanda slot 18. Plenum
20 essentially serves as a reservoir in which high pressure gas
equilibrates before being evenly distributed along the length of
the Coanda slot 18 via chamber 30. Conduit 36 can include a single
channel which connects the source of gas 24 to plenum 20,
alternatively a plurality of holes drilled into the lower surface
of the stabilizer can be employed. It is preferred that the
plurality of holes be spaced apart along the cross direction of the
body in order to distribute gas evenly into plenum 20.
[0030] The body of the stabilizer is preferably constructed of
non-corrosive metal or hard plastic. As shown in FIG. 1, in this
embodiment the body of the stabilizer includes a lower portion 34
onto which upper portions 32A, 32B are attached. Coanda slot 18
preferably traverses almost the entire width of the upper surface.
Preferably, slot 18 has a width (b) of about 3 mils (76 .mu.m) to 4
about mils (102 .mu.m). The distance (d) from the upper to lower
surfaces is preferably between about 100 .mu.m to 1000 .mu.m.
Preferably the backstep location (L) is about 1 mm to about 10 mm
from Coanda slot 18.
[0031] Any suitable gas can be employed in gas source 24 including
for example, air, helium, argon, carbon dioxide. For most
applications, the amount of gas employed is that which is
sufficient to discharge the gas at slot 18 at a velocity of about
50 m/s to about 80 m/s. This will maintain the web at a distance
ranging from about 400 .mu.m to about 800 .mu.m above the operative
surface of the stabilizer. As is apparent, by regulating the
velocity of the jet of gas exiting slot 18, one can adjust the
distance that the moving web is maintained above the operative
surface of the stabilizer.
[0032] As will be further demonstrated herein, a flat paper profile
in the machine direction of the stabilizer can be established with
the air clamp stabilizer of the present invention. It should be
noted that with the air clamp stabilizer, the paper profile
flatness is also maintained in the cross flow direction since the
configuration of the surface of the stabilizer is symmetric in this
dimension. One advantage is that the paper profile flatness can be
scaled arbitrarily in the cross flow direction. Indeed, the
dimensions of the air clamp stabilizer can be readily scaled to
accommodate the size, weight, speed, and other variable associated
with the moving web. Specifically, it will be appreciated, for
instance, that the air clamp stabilizer's (i) slot width (b) (ii)
curvature radius (R), (iii) depth of backstep (d), and (iv)
distance of the backstep from slot (L), can be optimized
systematically for a particular application and can be adapted
depending on the properties, e.g., speed and weight, of the web
material. Similarly, the gas jet velocity through the Coanda slot
can be adjusted.
[0033] In operation, the stabilizer is positioned below a
continuously moving web of material that is traveling from left to
right with respect to the configuration of the stabilizer shown in
FIG. 1. Gas, e.g., air, is supplied to plenum 20 and a jet of gas
is forced through the Coanda slot 18 which is then deflected around
curved surface 22. The curvature of the jet of air then attaches to
upper surface 12B and continues parallel to upper surface 12B. The
jet creates a lower pressure that generates a suction force that is
normal to surface 12B and an air bearing. Backstep 16 which is
located downstream of the direction of the airflow extending from
Coanda slot 18 promotes the creation of additional suction forces
primarily through jet expand and secondarily through vortex
formation, when the latter occurs. The web material moves parallel
over the stabilizer and rides on top of the air bearing.
[0034] FIGS. 2 and 3 illustrate another embodiment of the air clamp
stabilizer 40 that includes a central body member 42 that is
flanked by side supports 44 and 46. The central body member
includes a Coanda slot 48 and accompanying backstep 50. The first
side support 44 is secured to one side of the central body by
screws 52 that are threaded into holes 74 and 72. Second side
support 46 is similarly secured to the other side by screws 58 that
are threaded holes 76 and holes on the central body (not shown).
The side supports serve to seal the internal plenum and chamber as
further described herein. The stabilizer is preferably constructed
of stainless steel.
[0035] In this embodiment, the central body 42 is constructed as a
single, unitary structure as illustrated in the side view of the
central body shown in FIG. 4. The operative surface includes upper
surfaces 86A, 86B and lower surface 54. Internally, central body 42
includes an elongated plenum 64 that is in communication with a
narrower chamber 88 which has an opening that forms Coanda slot 56.
As is apparent, plenum 64 and chamber 88 are not two distinct
cavities within the central body rather they can represent two
regions of a single cavity that traverses the width (cross
direction) of the central body. A plurality of evenly spaced holes
(not shown) is drilled through the underside of the central body
and into plenum 64. The holes serve as gas inlets. Central body 42
further defines an elongated slot 66 under upper surface 86A that
traverses the width of the central body. Slot 66 also has an
opening 90 on one side thereby creating a cantilever or projecting
structure 60 above slot 66 and a base 62 below slot 66. As is
apparent, the size, i.e., width, of the gap of Coanda slot 56 can
be adjusted by moving edge 82 towards or away from upper surface
86B. As shown in FIG. 5, a rigid object 80 when inserted into the
slot 66 moves edge 82 forward to reduce the width of Coanda slot
56. (In one embodiment, a plurality of adjustable screws are
employed.) The narrow region 92 between slot 66 and chamber 88
functions as a fulcrum on which cantilever structure 60 pivots.
EXAMPLE 1
[0036] A stainless steel air clamp stabilizer having the
configuration shown in FIG. 1 was fabricated and tested.
Specifically, the stabilizer included a Coanda slot having a width
(b) of 0.1 mm (0.004 in) and a curvature radius (R) of 1.6 mm
(0.0625 in). In addition, the stabilizer had a backstep location
(L) 3 mm downstream of the slot and a backstep depth (d) of 0.5 mm.
Gas was supplied into plenum through three holes drilled into the
underside of the device. The air clamp was employed to support a
moving web of newsprint that was traveling at about 1790 m/min and
had a water weight of 68 grams per square meter (gsm). The term
"water weight" refers to the mass or weight of water per unit area
of the paper.
[0037] The contour of the stabilizer surface was measured prior to
operations. As depicted by the lower curve in FIG. 6, the vertical
position of the upper surface was set at 500 .mu.m above that of
the lower surface. The lower curve highlights the presence of the
Coanda slot located at about position -7 mm (corresponding the
first sharp decline on the lower curve) and the backstep located at
about position -4. During operations the paper sheet profile was
measured by scanning over the paper surface with a laser
triangulation sensor as the paper sheet was moved horizontally over
the surface of the air clamp stabilizer. As depicted by the upper
curve of FIG. 5, the fluctuating paper was pulled a distance of
about 1.5 mm toward the stabilizer surface by the suction force of
the stabilizer. The air pressure supplied to the Coanda slot was 40
psi. However, when the paper reached the backstep, the paper
contour becomes flat over a distance of more than 10 mm with a
slope of less than 0.1 degrees over this span. Because of the air
bearing, the paper did not touch the air clamp surface.
EXAMPLE 2
[0038] To demonstrate that incorporating a backstep downstream from
the Coanda slot was the cause of the of improved paper sheet
flatness, another stabilizer having the same Coanda slot as the
stabilizer of Example 1 but without any backstep was tested. The
conditions employed were the same as those for Example 1. As shown
in FIG. 6, the paper profile has a pronounced minimum close to the
location of the Coanda slot (indicated by the vertical hatched
line) with a sharp increase downstream. The flat area that was
obtained with the backstep (as shown in FIG. 5) is missing
altogether. This shows the significance of the backstep in order to
achieve sheet flatness.
EXAMPLE 3
[0039] The behavior of the air clamp stabilizer in response to
changes in web speed was also studied. The procedure of Example 1
was repeated for newsprint traveling at 800 m/min. and 2690 m/min.
FIG. 7 shows the paper sheet profiles 800 (curve A), 1790 (curve
B), and 2690 m/min. (curve C). As is apparent, curve B and the
stabilizer surface profile are identical to those of FIG. 5. The
data show that the paper sheet profile downstream of the stabilizer
is basically independent of the paper speed. Again the stabilized
flat areas extend over 10 mm and have slopes of less than 0.1
degrees at all three paper speeds.
EXAMPLE 4
[0040] As noted above, the optimal ranges of the geometric
dimensions for the air clamp stabilizer can be ascertained
experimentally or by computer simulation for different processes,
e.g., web materials. As an example, experiments were conducted to
observe the effects of adjusting the Coanda slot width to curvature
ratio on suction pressure. The suction pressure is the suction
force that is exerted on a sheet of paper placed over the
stabilizer. Specifically, three stabilizers each with a different
Coanda slot radius of curvature, i.e., 0.0625 in. (0.16 cm), 0.1875
in. (0.48 cm), and 0.3750 in. (0.96 cm) were tested as a function
of slot width that ranged from 0.003 in. (0.0076 cm) to 0.03 in.
(0.076 cm) at a constant supply air pressure for each. The
pressures were selected so as to result in jet attachment to the
operative surface of the stabilizer. Jet attachment is a necessary
condition for a working air clamp stabilizer. For instance, if the
radius of curvature is too small and/or the gap too large, the jet
of gas exiting the Coanda slot would detach from the operative
surface and not follow the curvature radius. Instead, the jet of
gas would traject essentially vertically from the Coanda slot and
actually push the paper away rather than exert a suction force
thereon.
[0041] The results are shown in FIG. 9 with curves A, B, and C,
representing the Coanda slots with curvature radii of 0.0625 in.,
0.1875 in, and 0.3750 in., respectively. As is apparent, the
highest suction force was achieved with stabilizers having the
smallest chosen curvature and the smallest slot width. The data
also suggest that the suction force was localized over a small area
adjacent to the Coanda slot. For other applications where a lower
suction force can be used, a larger radius with a possibly larger
slot width may be selected. The resulting stabilizer will also
spread the suction force over a greater area.
[0042] Web material that is supported by the inventive stabilizer
is preferably subject to measurement(s) with a non-contact
instrument, e.g., optical sensors. For example, the dry basis
weight or thickness of paper can be measured. Suitable instruments
and techniques for these procedures are described, for example, in
U.S. Pat. Nos. 4,767,935 "System and Method for Measurement of
Traveling Webs," U.S. Pat. No. 4,879,471 "Rapid-Scanning Infrared
Sensor," and U.S. Pat. No. 6,281,679 "Web Thickness Measurement
System," which are all assigned to the common assignee of the
instant application and which are incorporated herein by reference.
Another exemplary application is measuring properties of a web of
material that has been coated. For example, optical techniques for
measuring the gel point of a liquid material coated on paper is
described in U.S. Pat. No. 6,191,430 "Gel Point Sensor," which is
assigned to the common assignee of the instant application and
which is incorporated herein by reference.
[0043] While the advantages of the air clamp stabilizer have been
illustrated in association with the manufacture of paper, it is
understood that the air clamp stabilizer can be employed in any
environment where a moving web of material must be stabilized to
establish a flat profile for measurement or simply for ease of
processing, e.g., packaging, during manufacturing. For example, the
stabilizer can be readily implemented in the manufacture of
fabrics.
[0044] Although only preferred embodiments of the invention are
specifically disclosed and described above, it will be appreciated
that many modifications and variations of the present invention are
possible in light of the above teachings and within the purview of
the appended claims without departing from the spirit and intended
scope of the invention.
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